Optical disc and its manufacturing method

ABSTRACT

On a replica substrate la, a reflection layer  11 , a first dielectric layer  12  made of ZnS—SiO 2 , a recording layer  13  made of a phase change type recording material, and a second dielectric layer  14  made of ZnS—SiO 2  are successively formed. In addition, a reaction protection layer  15  made of Si 3 N 4  or SiO 2  is formed on the second dielectric layer  14 . As a result, an information signal portion  1   c  is composed. A light transmissivity sheet is formed through an adhesive layer so that the light transmissivity sheet coats an information signal portion  1   c . As a result, a light transmission layer is composed. When the reaction protection layer  15  is not formed, a reaction protection resin layer made of an ultraviolet ray setting resin is formed so that the reaction protection resin layer coats the information signal portion  1   c.

TECHNICAL FIELD

[0001] The present invention relates to an optical disc and afabrication method thereof, in particular, to an optical disc of which alight transmission layer formed on a disc substrate is composed of alight transmissivity sheet and an adhesion layer.

BACKGROUND ART

[0002] In recent years, in the information recording field, a variety ofattempts of research and development have be made for the informationrecording system. In the optical information recording system, data canbe recorded and reproduced contact-freely. As one advantage, the opticalinformation recording system can accomplish a recording density morethan ten times higher than the conventional magnetic recording system.As another advantage, the optical information recording system can applyto individual memory types such as the read-only type, the write-oncetype, the rewritable type, and so forth. Thus, as a system thataccomplishes inexpensive and large-capacity files, it has beenconsidered that the optical information recording system will be widelyused from industries to homes.

[0003] Among those, digital audio discs (DAD) and optical video discs,which are optical discs of read-only memory type, have become common.

[0004] In an optical disc such as a digital audio disc, a reflectionfilm that is a metal thin film such as an aluminum (Al) film is formedon an optical disc substrate that is a transparent substrate on which anuneven pattern such as pits and grooves that represent an informationsignal is formed. In addition, a protection film that protects thereflection film against moisture (H₂O) and oxygen (O₂) in the atmosphereis formed on the reflection film. When an information signal isreproduced from the optical disc, read light such as laser light isradiated from the optical disc substrate side to the uneven pattern.Corresponding to the difference of reflectance of the incident light andthe reflected light of the read light, the information signal isdetected.

[0005] When such an optical disc is produced, an optical disc substratehaving an uneven pattern is formed by the injection molding method.Thereafter, a reflection film made of a metal thin film is formed on theoptical disc substrate by the vacuum evaporation method. Thereafter, anultraviolet ray setting resin is coated on the reflection film. As aresult, the protection film has been formed.

[0006] In the aforementioned optical information recording system, inrecent years, an increase of recording density has been required. Tosatisfy that, a technology for decreasing the diameter of the spot ofthe read light with an increased numerical aperture (NA) of an objectivelens through which the read light is radiated from an optical pickup hasbeen proposed. According to the technology, while the NA of an objectivelens used to reproduce data from a conventional digital audio disc is0.45, the NA of an objective lens used to reproduce data from an opticalvideo disc such as a DVD (Digital Versatile Disc) that has a recordingcapacity six to eight times higher than that of the digital audio discis around 0.60. As a result, the diameter of the spot is decreased.

[0007] As the NA of the objective lens is increased, the disc substrateof the optical disc should be thinned so as to transmit the radiatedread light. This is because the tolerable amount of the deviation angle(tilt angle) of the optical axis of the optical pickup against thevertical line of the disc surface becomes small. The tilt angle issubject to influences of aberration and double refraction due to thethickness of the substrate. Thus, the substrate is thinned so that thetilt angle becomes as small as possible. For example, the thickness ofthe substrate of the aforementioned digital audio disc is around 1.2 mm.In contrast, the thickness of the substrate of an optical video discsuch as a DVD, which has a recording capacity six to eight times higherthan the digital audio disc, is around 0.6 mm.

[0008] However, in consideration of the increasing needs of highrecording density, the substrate should be further thinned. To satisfythat, another type optical disc has been proposed. In this optical disc,an uneven pattern is formed on one main plane of a substrate as aninformation signal portion. A reflection film and a light transmissionlayer, which is a thin film that transmits light, are successivelylayered. Read light is radiated from the light transmission layer side.As a result, an information signal is reproduced. In such an opticaldisc, of which read light is radiated from the light transmission layerside and thereby an information signal is reproduced, the film thicknessof the light transmission layer is decreased so that the optical disccan conform with a large NA of an objective lens.

[0009] However, when the light transmission layer is thinned, it becomesdifficult to form a light transmission layer with a thermoplastic resinby the injection molding method, which is used in a conventional opticaldisc producing method. In other words, in the conventional technology,it is very difficult to form a light transmission layer that has athickness of around 0.1 mm and that has small double refraction and goodtransparency.

[0010] To solve such a problem, a method for forming a lighttransmission layer with an ultraviolet ray setting resin. In thismethod, however, when the light transmission layer is formed with theultraviolet ray setting resin, it is very difficult to keep the filmthickness of the light transmission layer constant on the surface of thesubstrate. Thus, it is difficult to stably reproduce the informationsignal.

[0011] Alternatively, the light transmission layer may be formed byadhering a thermoplastic resin sheet having a film thickness of 0.1 mmto the surface of the substrate by the roller pressing method. However,in this method, when the sheet is pressed, the sheet deforms and theadhesive agent protrudes to the reading surface side. Thus, it isdifficult to form the light transmission layer with an equal filmthickness. It is much difficult to stably reproduce the informationsignal.

[0012] Thus, to solve those problems, the inventors of the presentinvention have thought of a method for forming a light transmissionlayer of which a sheet composed of an adhesive layer and a lighttransmission layer is adhered to an information signal portion of asubstrate. As a result, a method for adhering a light transmission layerto a substrate using an adhering device composed of an elastic pad and ametal plane stage has been proposed. Next, with reference to anaccompanying drawing, the adhering device will be practically described.

[0013] In other words, as shown in FIG. 1, in a conventional adheringdevice, a fixed stage 101 and a movable stage 102 are disposed at theiropposite positions.

[0014] The fixed stage 101 is used to hold a sheet 103. Thus, the fixedstage 101 is structured so that it can hold the sheet 103. In otherwords, a vertically movable pin 105 that is protruded from the fixedstage 101 and buried therein is disposed in the fixed stage 101. Thevertically movable pin 105 faces the movable stage 102. The diameter ofthe vertically movable pin 105 is the same as the diameter of athrough-hole 103 a of the sheet 103. The through-hole 103 a of the sheet103 is fit to the vertically movable pin 105. As a result, the sheet 103can be held on the fixed stage 101. A substrate alignment pin 106cylindrically protrudes at an upper portion of the vertically movablepin 105. The diameter of the substrate alignment pin 106 is almost thesame as the diameter of a center hole 104 a of a disc substrate 104.While the substrate alignment pin 106 aligns the center of the discsubstrate 104, the vertically movable pin 105 holds the disc substrate104. On the fixed stage 101, the sheet 103 is fit to the substratealignment pin 106 so that the sheet 103 is hold by a shoulder portion ofthe vertically movable pin 105.

[0015] A pad 107 made of an elastic member such as rubber is disposed onan inner plane of the movable stage 102 so that the pad 107 faces thefixed stage 101. The pad 107 is formed in a conical shape. The planeside of the conical shape is secured to the inner plane of the movablestage 102.

[0016] When the disc substrate 104 and the sheet 103 are adhered by suchan adhering device, the through-hole 103 a of the sheet 103 is fit tothe vertically movable pin 105 disposed so that the sheet 103 is held onthe fixed stage 101. At that point, an adhesive plane 103 b of the sheet103 is disposed so that it faces the movable stage 102. Thereafter, thecenter hole 104 a of the disc substrate 104 is fit to the substratealignment pin 106 so that the center hole 104a is held on the shoulderportion of the vertically movable pin 105. At that point, the discsubstrate 104 is held on the vertically movable pin 105 so that arecording plane 104 b that has an information signal portion faces theadhesive plane 103 b that has an adhesive layer.

[0017] Thereafter, the movable stage 102 is moved toward the fixed stage101 (downwards in FIG. 1). With the pad 107, the substrate alignment pin106 is pressed. Thereafter, the vertically movable pin 105 is moved inthe fixed stage 101 through the disc substrate 104. As a result, theclearance between the disc substrate 104 and the sheet 103 graduallybecomes small. Finally, the disc substrate 104 and the sheet 103 arepress-fit. As a result, the recording plane 104 b and the adhesive plane103 b are adhered. After they have been stably press-fit, the movablestage 102 is moved in the direction that it is apart from the fixedstage 101. Thereafter, with a predetermined conveying device (notshown), the disc substrate 104 and the sheet 103, which have beenpress-fit, are removed from the fixed stage 101.

[0018] As a result, the disc substrate 104 and the sheet 103 have beenadhered. An optical disc of which a light transmission layer has beenformed on the recording plane 104 b of the disc substrate 104 has beenproduced.

[0019] An optical disc having a light transmission layer formed in sucha manner can conform with a large NA of the objective lens, which isused to reproduce data from the optical disc.

[0020] However, various experiments and evaluations that the inventorshave repeatedly conducted show that such an optical disc has thefollowing problem.

[0021] In other words, when a phase change type recording material isused for an information signal portion in an optical disc on which alight transmission layer is formed, as the material of the outermostlayer of the information signal portion, a mixture (ZnS—SiO₂) of zincsulfide and silicon oxide, which is a transparent dielectric, arenormally used. A light transmissivity sheet is adhered onto theinformation signal portion having the ZnS—SiO₂ layer as the outermostlayer through an adhesive layer made of a pressure-sensitive adhesiveagent is disposed.

[0022] However, the results of which the inventors of the presentinvention have conducted acceleration tests for a plurality of opticaldiscs having such a light transmission layer and measured reflectancethereof show that the reflectance thereof deteriorates. When thereflectance deteriorates, it will become difficult to record andreproduce an information signal to and from an optical disc having alight transmission layer with high accuracy.

[0023] Therefore, an object of the present invention is to provide anoptical disc of which a light transmissivity sheet has been adhered onone main plane of a substrate through an adhesive layer, in particular,an optical disc that suppresses the variation of reflectance thereof,that suppresses the variation of reflectance on therecording/reproducing plane thereof, that conforms with a large NA of anobjective lens used to record/reproduce data, and that has a lighttransmission layer that has small double refraction, high transparency,and equal film thickness and an optical disc producing method thatallows the production yield to improve.

DISCLOSURE OF THE INVENTION

[0024] The inventors of the present invention have intensively madeefforts to solve the aforementioned problems of the prior art. Theoutline will be described in the following.

[0025] As described above, according to the knowledge that the inventorsof the present invention have obtained, when an optical disc is producedby adhering a light transmissivity sheet and a disc substrate through anadhesive layer made of a pressure-sensitive adhesive agent, thereflectance varies in each of a plurality of optical discs. In addition,the reflectance varies on the recording/reproducing plane. Furtherobservations and experiments that the inventors of the present inventionhave conducted for those optical discs show that the light transmissionlayer has yellowish discolored, which causes the reflectance to vary.

[0026] The inventors of the present invention have further pursuedcauses of the yellowish discoloring of the light transmission layer andevaluated them. As a result, the inventors of the present invention havesupposed that a chemical reaction of a dielectric layer, which is madeof ZnS—SiO₂ used for a laminate film that composes the informationsignal portion of the optical disc, and the pressure sensitive adhesiveagent causes the light transmission layer to yellowish discolor. Inconsideration of the knowledge of the inventors of the present inventionalong with the supposed cause, it seems that zinc (Zn) mainly affectsthe pressure-sensitive adhesive agent is high and so does sulfur (S).

[0027] In the information signal portion of the optical disc, however,to have sufficient recording characteristic and so, as the material of adielectric film that sandwiches the recording layer, ZnS—SiO₂ ispreferably used. When the dielectric film is made of other than ZnS—SiO₂as the material of the dielectric film, which sandwiches the recordinglayer, there is a possibility that a chemical reaction of thepressure-sensitive adhesive agent and the adhesive layer might cause theadhesive layer to discolor. In addition, the material of the dielectricfilm is an important structural element in various characteristics suchas a recording/reproducing characteristic of the optical disc. Thus,since the material of the dielectric film has many restrictions toimprove characteristics, it is very difficult to replace the material ofthe dielectric film with another one.

[0028] The inventors of the present invention have repeatedly evaluateda method for preventing the adhesive layer of the light transmissionlayer from discoloring, in particular, yellowish discoloring and thoughtof a method of which a material that does not chemically react with thepressure-sensitive adhesive agent, which composes the adhesive layer, isinterposed between the information signal portion and thepressure-sensitive adhesive agent. In addition, the inventors of thepresent invention have evaluated and experiments various materials thatdo not chemically react with the pressure-sensitive adhesive agent andhas a knowledge that as such a material inorganic materials such asdielectrics for example silicon nitride and silicon oxide and organicmaterials such as ultraviolet ray setting resin are suitable.

[0029] According to the evaluated result that the inventors of thepresent invention have intensively conducted, to accomplish goodreflectance, it is preferred that on the upper layer of the conventionalinformation signal portion of the optical disc, on a lower plane of theadhesive layer of the light transmission layer, a reaction protectionlayer made of a dielectric inorganic material or an organic materialshould be disposed. As the material, silicon nitride, silicon oxide, oran ultraviolet ray setting resin is more suitable.

[0030] To accomplish the aforementioned object, a first aspect of thepresent invention is an optical disc having an information signalportion composed of a plurality of layers and configured to recordand/or reproduce an information signal and a light transmission layerconfigured to transmit laser light used to record and/or reproduce theinformation signal, the information signal portion and the lighttransmission layer being formed on one main plane of a substrate of theoptical disc,

[0031] wherein the light transmission layer comprises at least a sheethaving light transmissivity and an adhesive layer for adhering the sheetto the main plane of the substrate, and

[0032] wherein a reaction protection layer is formed on the informationsignal portion so that the reaction protection layer faces the adhesivelayer.

[0033] According to the first aspect of the present invention, thereaction protection layer is typically made of a dielectric. Thedielectric is preferably silicon nitride (SiN, Si₃N₄). The filmthickness of the reaction protection layer made of silicon nitride ispreferably 2 nm or larger. The dielectric that composes the reactionprotection layer may be silicon oxide (SiO₂). The film thickness of thereaction protection layer made of silicon oxide is preferably 2 nm orlarger.

[0034] According to the first aspect of the present invention, the filmthickness of the light transmission layer is typically in the range from90 μm to 110 μm.

[0035] A second aspect of the present invention is an optical dischaving an information signal portion composed of a plurality of layersand configured to record and/or reproduce an information signal and alight transmission layer configured to transmit laser light used torecord and/or reproduce the information signal, the information signalportion and the light transmission layer being formed on one main planeof a substrate of the optical disc,

[0036] wherein the light transmission layer comprises a sheet havinglight transmissivity and an adhesive layer configured to adhere thesheet to the main plane of the substrate, and

[0037] wherein a reaction protection layer made of an organic materialis formed between the information signal portion and the adhesive layer.

[0038] According to the second aspect of the present invention, theorganic material is typically an ultraviolet ray setting resin. Theultraviolet ray setting resin preferably contains a solvent. The solventis preferably methoxypropanol. Alternatively, another solvent may beused.

[0039] According to the second aspect of the present invention, thedistribution of the film thickness of the reaction protection layer in aregion of at least the information signal portion is typically 1 μm orsmaller.

[0040] According to the second aspect of the present invention, the filmthickness of the light transmission layer is typically in the range from90 μm to 110 μm.

[0041] According to the second aspect of the present invention,typically, the organic material is an ultraviolet ray setting resin,which is hardened by the radiation of an ultraviolet ray. In reality,the organic material is an ultraviolet ray hardening resin of forexample acrylate group, thiol group, epoxy group, or a silicon group.When an ultraviolet ray setting resin is used as the reaction protectionlayer, typically, an ultraviolet ray is radiated to at least theultraviolet ray setting resin and then hardened. As a result, thereaction protection layer is formed. According to the present invention,a suitable hardening method can be selected for a resin selected as anorganic material.

[0042] A third aspect of the present invention is an optical disc havingan information signal portion configured to record and/or reproduce aninformation signal and a light transmission layer configured to transmitlaser light used to record and/or reproduce the information signal, theinformation signal portion and the light transmission layer being formedon one main plane of a substrate of the optical disc,

[0043] wherein the light transmission layer comprises a sheet havinglight transmissivity and an adhesive layer configured to adhere thesheet to the main plane of the substrate,

[0044] wherein the information signal portion comprises a reflectionlayer configured to reflect the laser light, a first dielectric layer, arecording layer configured to record the information signal, and asecond dielectric layer successively formed from the substrate, and

[0045] wherein the film thickness of the second dielectric layer isdesignated so that the reflectance of the laser light on a flat plane ofthe substrate is 15% or larger.

[0046] According to the present invention, to allow the reflectance oflaser light to be 15% or larger, the film thickness of the seconddielectric layer is typically in the range from 45 nm to 90 nm or in therange from 130 nm to 175 nm.

[0047] According to the third aspect of the present invention, thesecond dielectric layer is typically made of a mixture of zinc sulfideand silicon oxide.

[0048] A fourth aspect of the present invention is an optical discproducing method, comprising the steps of:

[0049] forming an information signal portion configured to record and/orreproduce an information signal on a main plane of a substrate; and

[0050] adhering a light transmissivity sheet configured to transmitlaser light used to record and/or reproduce the information signal in aregion that covers the information signal portion through an adhesivelayer,

[0051] wherein a reaction protection layer is formed on the outermostlayer of the information signal portion.

[0052] According to the fourth aspect of the present invention, thereaction protection layer is typically made of a dielectric. In reality,the dielectric is silicon nitride or silicon nitride. The film thicknessof the reaction protection layer made of silicon nitride or siliconoxide is 2 nm or larger.

[0053] According to the fourth aspect of the present invention, theadhesive layer is typically made of a pressure-sensitive adhesive agent.

[0054] According to the fourth aspect of the present invention, the filmthickness of the light transmission layer is preferably in the rangefrom 90 μm to 110 μm.

[0055] A fifth aspect of the present invention is an optical discproducing method, comprising the steps of:

[0056] forming an information signal portion configured to record and/orreproduce an information signal on a main plane of a substrate; and

[0057] adhering a light transmissivity sheet configured to transmitlaser light used to record and/or reproduce the information signal in aregion that covers the information signal portion through an adhesivelayer,

[0058] wherein after the information signal portion forming step, beforethe light transmissivity sheet adhering step, a reaction protectionlayer made of an organic material is formed on at least an upper layerof the information signal portion.

[0059] According to the fifth aspect of the present invention, to coatan organic material such as an ultraviolet ray setting resin on all theplane of at least the information signal portion, it is preferred thatafter liquid ultraviolet ray setting resin is dripped on the substrate,the substrate is rotated about the center axis of the disc plane. Inother words, the ultraviolet ray setting resin is formed so that itcoats the information signal portion by for example the spin coatmethod. When the ultraviolet ray setting resin contains a solvent, afterit is coated by the spin coat method, the solvent is evaporated.

[0060] According to the fifth aspect of the present invention, theorganic material is typically an ultraviolet ray setting resin. Todecrease the difference between the inner and outer circumferential filmthicknesses of the substrate, the ultraviolet ray setting resin containsa solvent. According to the fifth aspect of the present invention, thedistribution of the film thickness of the reaction protection layer in aregion for at least the information signal portion is preferably 1 μm orsmaller.

[0061] According to the fifth aspect of the present invention, the filmthickness of the light transmission layer is typically in the range from90 μm to 110 μm.

[0062] According to the present invention, the film thickness of theinformation signal portion is preferably in the range from 183 nm to 313nm.

[0063] According to the present invention, to suppress the chemicalreaction of the adhesive layer and the outermost layer of theinformation signal layer and prevent the adhesive layer fromdiscoloring, the reaction protection layer is typically made of adielectric. To securely suppress the discoloring of the adhesive layer,the dielectric is preferably silicon nitride (Si₃N_(4−x) (where 0×1,typically Si₃N₄) or silicon oxide (SiO_(x) (where 1×2, typically SiO₂ orSiO). The dielectric may be aluminum nitride (AlN_(x) (where 0.5×1,typically AlN), aluminum oxide (Al₂O_(3−x) (where 0×1, typically alumina(Al₂O₃)), magnesium oxide (MgO), yttrium oxide (Y₂O₃), magnesiumaluminum oxide (MgAl₂O₄), titanium oxide (TiOx (where 1×2, typicallyTiO₂), barium titanium oxide (BaTiO₃), strontium titanium oxide(SrTiO₃), tantalum oxide (Ta₂O_(5−x) (where 0×1, typically Ta₂O₅),germanium oxide (GeO_(x)) (where 1×2), silicon carbide (SiC), zincsulfide (ZnS), lead sulfide (PbS), Ge—N, Ge—N—O, Si—N—O, calciumfluoride (CaF), lanthanum fluoride (LaF), magnesium fluoride (MgF₂),sodium fluoride (NaF), titanium fluoride (TiF₄), or the like. Moreover,a material whose principal component is one of those materials or amixture of these materials for example AlN—SiO₂ may be used.

[0064] According to the present invention, the substrate typically has adisc shape. In addition, the light transmissivity sheet has a discshape. According to the present invention, to form a light transmissionlayer having a light transmissivity sheet, an adhesive layer is disposedon one plane of a sheet that has been cut in a disc shape. By adheringthe substrate and the sheet through the adhesive layer, a lighttransmission layer is formed on the substrate. According to the presentinvention, typically, the inner diameter of the disc shaped sheet isequal to or larger than the inner diameter of the disc shaped substrate.In addition, the outer diameter of the disc shaped sheet is equal to orsmaller than the disc shaped substrate.

[0065] According to the present invention, the adhesive layer istypically made of a Pressure-Sensitive Adhesive agent (PSA).

[0066] According to the present invention, to minimize the warp anddistortion of the optical disc to be produced, the light transmissivitysheet is preferably made of the same material as the substrate. Thethickness of the light transmissivity sheet is typically smaller thanthe thickness of the substrate. In reality, the thickness of the lighttransmissivity sheet is in the range from 30 μm to 150 μm. In addition,according to the present invention, the disc substrate is made of aresin having a low moisture absorbing power such as polycarbonate (PC)or cycloolefin polymer. The light transmissivity sheet is preferablymade of the same material as the disc substrate. The substrate may befor example a substrate made of a metal such as aluminum, a glasssubstrate, or a substrate made of polyolefin, polyimide, polyamide,polyphenylene sulfide, polyethylene terephthalate (PET), or the like.The light transmissivity sheet is typically made of polycarbonate resin.Alternatively, the light transmissivity sheet may be made of anothermaterial.

[0067] According to the present invention, to prevent a foreign matterpresent on the sheet holding plane of the adhering device from flawingor denting the light transmissivity sheet, the sheet is preferablycomposed of a light transmissivity sheet, an adhesive layer formed onone place of the light transmissivity sheet, and a protection layerformed on the other plane of the light transmissivity sheet. Inaddition, the protection layer is preferably made of a polyethyleneterephthalate (PET) sheet, a polyethylene naphthalate (PEN) sheet, orthe like. More practically, a second adhesive agent is coated on atleast one plane of the PET sheet or the PEN sheet. The plane on whichthe second adhesive agent has been coated is adhered on one plane of thelight transmissivity sheet. As a result, a sheet that is adhered to thedisc substrate is obtained.

[0068] According to the present invention, the light transmissivitysheet is typically made of a non-magnetic material that can transmitlaser light radiated from a GaN semiconductor laser (wavelength of lightemission: 400 nm band, blue light emission), a ZnSe semiconductor laser(wavelength of light emission: 500 nm band, green light emission), anAlGaInP semiconductor laser (wavelength of light emission: around 635 to680 nm, red light emission), or the like, which is used torecord/reproduce at least an information signal. In reality, the lighttransmissivity sheet is made of a thermoplastic resin such aspolycarbonate that has a light transmission characteristic.

[0069] The present invention can be preferably applied to an opticaldisc having a thin light transmission layer. In other words, the presentinvention can be applied to the so-called DVR-red, of which aninformation signal is recorded and reproduced using a semiconductorlaser whose wavelength of light emission is around 650 nm or theso-called DVR-blue, of which an information signal is recorded andreproduced with a semiconductor laser whose wavelength of light emissionis around 400 nm. Preferably, using an objective lens whose NA is ashigh as around 0.85 having two lens elements disposed in series, the DVRrecords an information signal. Practically, one side of the optical dischas a recording capacity of around 22 GB. The optical disc according tothe present invention is an optical disc such as a DVR, which is housedin a cartridge. However, the present invention is not limited to anoptical disc that is housed in a cartridge.

[0070] In the optical disc and the producing method thereof according tothe present invention, a light transmission layer is composed of atleast a light transmissivity sheet and an adhesive layer that adheresthe light transmissivity sheet to a main plane of a substrate. A layerthat composes a plane that contacts the adhesive layer of theinformation signal portion is composed of a reaction protection layer.As a result, the adhesive layer and a dielectric layer that composes theinformation signal portion can be prevented from chemically reactingwith each other.

BRIEF DESCRIPTION OF DRAWINGS

[0071]FIG. 1 is a schematic diagram showing a conventional adheringdevice that is used to adhere a disc substrate and a sheet;

[0072]FIG. 2 is a sectional view showing an optical disc according to afirst embodiment of the present invention;

[0073]FIG. 3 is a sectional view showing a disc substrate according tothe first embodiment of the present invention;

[0074]FIG. 4 is a sectional view showing the detail of an informationsignal portion of the disc substrate according to the first embodimentof the present invention;

[0075]FIG. 5 is a sectional view showing a sheet used to form a lighttransmission layer according to the first embodiment of the presentinvention;

[0076]FIG. 6 is a schematic diagram showing an adhering device thatadheres the disc substrate and the sheet according to the firstembodiment of the present invention;

[0077]FIG. 7 is a graph showing a film thickness dependency of a seconddielectric layer to the reflectance of a mirror portion of the opticaldisc according to the first embodiment of the present invention;

[0078]FIG. 8 is a sectional view showing an optical disc according to athird embodiment of the present invention;

[0079]FIG. 9 is a sectional view showing a disc substrate according tothe third embodiment of the present invention;

[0080]FIG. 10 is a schematic diagram for explaining a method for forminga reaction protection resin layer according to the third embodiment ofthe present invention;

[0081]FIG. 11 is a schematic diagram for explaining the method forforming the reaction protection resin layer according to the thirdembodiment of the present invention; and

[0082]FIG. 12 is a schematic diagram for explaining the method forforming the reaction protection resin layer according to the thirdembodiment of the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

[0083] Next, with reference to the accompanying drawings, embodiments ofthe present invention will be described. In the drawings with which theembodiments will be described, similar portions are denoted by similarreference numerals.

[0084] First of all, an optical disc according to a first embodimentwill be described. FIG. 2 shows the optical disc according to the firstembodiment of the present invention.

[0085] As shown in FIG. 2, in the optical disc according to the firstembodiment, a center hole 1 b is formed at a center portion of a replicasubstrate 1 a of a disc substrate 1. One main plane of the discsubstrate 1 is unevenly formed. An information signal portion 1 c isformed on the main plane of the disc substrate 1. In addition, a lighttransmission layer 2 is disposed on the disc substrate 1. The lighttransmission layer 2 is composed of a light transmissivity sheet 2 a andan adhesive layer 2 b that has been adhered thereto. A through-hole 2 cis formed at a center portion of the light transmission layer 2.

[0086] A circular clamp region 3 is set around the through-hole 2 c on alower main plane of the light transmissivity sheet 2 a of the lighttransmission layer 2. The innermost diameter of the circular clampregion 3 is for example 23 mm. The outermost diameter of the circularclamp region 3 is for example 33 mm. On the lower main plane of thelight transmissivity sheet 2 a of the light transmission layer 2 in thecircular clamp region 3, a clamp reference plane 3 a at which theoptical disc is clamped or held by a spindle of a recording andreproducing device (both are not shown) is set. Since the lighttransmissivity sheet 2 a has been adhered to the lower main plane of thedisc substrate 1 through the adhesive layer 2 b, the diameter of thethrough-hole 2 c is designated equal to or larger than the diameter ofthe center hole 1 b of the disc substrate 1. For example, the diameterof the through-hole 2 c is designated 15 mm or larger. In addition,since the clamp reference plane 3 a is set on the lower main plane ofthe light transmissivity sheet 2 a of the light transmission layer 2,the diameter of the through-hole 2 c is equal to or smaller than theinnermost diameter of the circular clamp region 3. In reality, thediameter of the through-hole 2 c is for example 23 mm or smaller.

[0087] Next, a method for producing the optical disc according to thefirst embodiment will be described. FIG. 3 shows a disc substrate thatis a holding member of the optical disc. FIG. 4 shows the detail of thedisc substrate. FIG. 5 shows a sheet adhered to the disc substrate.

[0088] In the optical disc producing method according to the firstembodiment, as shown in FIG. 3, a disc substrate 1 on which a lighttransmission layer is formed is prepared. In the disc substrate 1, acenter hole 1 b is formed at a center portion of a replica substrate 1a. An information signal portion 1 c is formed on a lower main plane ofthe disc substrate 1. The lower main plane is unevenly formed.

[0089] The replica substrate 1 a is produced by the injection moldingmethod using a predetermined stamper. The thickness of the replicasubstrate 1 a is in the range from for example 0.6 to 1.2 mm. As thematerial of the replica substrate 1 a, for example a resin that has alow moisture absorption property such as polycarbonate or cycloolefinpolymer (for example, ZEONEX, which is a trademark of Nihon Zeon) isused. The replica substrate 1 a may be for example a substrate made of ametal such as aluminum, a glass substrate, or a substrate made ofpolyolefin, polyimide, polyamide, polyphenylene sulfide, polyethyleneterephthalate, or the like. In addition, on the uneven portion formed onthe lower main plane of the replica substrate 1 a, a recording film, areflection film, and so forth are formed. Those films compose theinformation signal portion 1 c. The information signal portion 1 c iscomposed of a reflection film, a film made of a magneto-opticalmaterial, a film made of a phase change material, or an organic colormatter film. Among those, as the material of the reflection film, forexample an Al alloy is used. In reality, when the optical disc as thefinal product is a read-only memory (ROM) optical disc, the informationsignal portion 1 c is composed of a single layer film or a laminate filmthat has at least a reflection layer made of for example an Al alloy.When the optical disc as the final product is a rewritable optical disc,the information signal portion 1 c is composed of a single layer film ora laminate film that has at least a film made of a magneto-opticalmaterial or a film made of a phase-change material. When the opticaldisc as the final product is a write-once type optical disc, theinformation signal portion 1 c is composed of a single layer film or alaminate film that has at least a film made of an organic color mattermaterial.

[0090] As shown in FIG. 4, in the disc substrate 1 according to thefirst embodiment, a polycarbonate (PC) substrate that has a thickness offor example 1.1 mm and that has a disc shape is used as the replicasubstrate la. The diameter (outer diameter) of the replica substrate 1 ais for example 120 mm. The aperture (inner diameter) of the center hole1 b is for example 15 mm. On a reflection layer 11, a first dielectriclayer 12, a recording layer 13, a second dielectric layer 14, and areaction protection layer 15 are successively formed. Those layerscompose the information signal portion 1 c.

[0091] As shown in FIG. 5, a sheet 4 as the light transmission layer 2is composed of a light transmissivity sheet 2 a and an adhesive layer 2b made of a pressure-sensitive adhesive agent (PSA) coated on one planeof the light transmissivity sheet 2 a. As with the disc substrate 1, thesheet 4 is cut in a disc shape. At a center portion of the sheet 4, athrough-hole 2 c is formed. The diameter (outer diameter) of the sheet 4is designated almost the same as or smaller than the outer diameter ofthe disc substrate 1. In reality, the diameter of the sheet 4 is forexample 120 mm. The diameter (inner diameter) of the through-hole 2 c isdesignated equal to or larger than the aperture of the center hole 1 b.The innermost diameter of the circular clamp region 3 is designatedequal to or smaller than the innermost diameter of the circular clampregion 3 (for example, 23 mm). The diameter of the through-hole 2 c isfor example 23 mm.

[0092] The light transmissivity sheet 2 a of the sheet 4 is made of athermoplastic resin that has light transmissivity that satisfies atleast an optical characteristic that can transmit laser light used forrecording/reproducing. The material of the thermoplastic resin is closeto the material of the replica substrate 1 a in heat resistancedimension stability, coefficient of thermal expansion, or coefficient ofmoisture absorption expansion. In reality, the thermal plastic resin isa methacrylic resin such as polycarbonate (PC) or polymethylmethacrylate. The thickness of the light transmissivity sheet 2 a ispreferably designated in the range from 50 to 100 μm, more preferably inthe range from 60 to 80 μm. According to the first embodiment, since thelight transmissivity sheet 2 a is adhered to one main plane of the discsubstrate 1 through the adhesive layer 2 b made of a pressure-sensitiveadhesive agent (PSA), the thickness of the light transmissivity sheet 2a is designated for example 70 μm. The thickness of the lighttransmissivity sheet 2 a is designated depending on the wavelength oflaser light used for recording/reproducing an information signal and adesired film thickness of the light transmission layer 2.

[0093] The PSA, which composes the adhesive layer 2 b, is for exampleacrylic resin. The thickness of the adhesive layer 2 b is for example 30μm. However, the thickness of the adhesive layer 2 b and the material ofthe pressure-sensitive adhesive agent are designated depending on thedesired film thickness of the light transmission layer 2 and thewavelength of the laser light used for recording/reproducing theinformation signal. While the sheet 4 is stocked, a protection film islaminated on the adhesive layer 2 b of the sheet 4.

[0094] Next, a method for adhering the disc substrate 1 and the sheet 4will be described.

[0095] First of all, an adhering device used to adhere the discsubstrate 1 and the sheet 4 will be described. FIG. 6 shows the adheringdevice according to the first embodiment.

[0096] As shown in FIG. 6, in the adhering device according to the firstembodiment, a fixed stage 21 and a movable stage 22 are disposed attheir opposite positions.

[0097] The fixed stage 21 is structured so that it can hold a sheet 4.In other words, in the fixed stage 21, a vertically movable pin 23 thatis protruded from the fixed stage 21 and buried therein is disposed at aportion that faces the movable stage 22. The diameter of the verticallymovable pin 23 is the same as the diameter of the through-hole 2 c ofthe sheet 4. The through-hole 2 c of the sheet 4 is fit to thevertically movable pin 23. The sheet 4 is held on the fixed stage 21. Asubstrate alignment pin 24 that protrudes in a cylinder shape isdisposed at an upper portion of the vertically movable pin 23. Thediameter of the substrate alignment pin 24 is almost the same as thediameter of the center hole 1 b of the disc substrate 1. While thesubstrate alignment pin 24 is aligned with the center of the discsubstrate 1, the disc substrate 1 is held with the vertically movablepin 23. On the fixed stage, the sheet 4 is fit to the vertically movablepin 23 so that the sheet 4 is held. While the disc substrate 1 is fit tothe substrate alignment pin 24, the disc substrate 1 is held by ashoulder portion of the vertically movable pin 23.

[0098] On a lower plane of the movable stage 22, a pad 25 made of anelastic member for example rubber is disposed so that the pad 25 facesthe fixed stage 21. The pad 25 has a circular cone shape. The plane sideof the circular cone shape of the pad 25 is secured to the lower planeof the movable stage 22.

[0099] When the disc substrate 1 and the sheet 4 are adhered by theadhering device according to the first embodiment, the through-hole 2 cof the sheet 4 is fit to the vertically movable pin 23 so that the sheet4 is held on the fixed stage 21. At that point, the sheet 4 is placed sothat the adhesive layer 2 b faces the movable stage 22. Thereafter, thecenter hole 1 b of the disc substrate 1 is fit to the substratealignment pin 24 so that the disc substrate 1 is held on the shoulderportion of the vertically movable pin 23. At that point, the discsubstrate 1 is held by the vertically movable pin 23 so that theinformation signal portion 1 c that has the information signal portionfaces the adhering plane of the adhesive layer 2 b.

[0100] Thereafter, the movable stage 22 is moved toward the fixed stage21 (downwards in FIG. 6). With the pad 25, the substrate alignment pin24 is pressed. Thereafter, the vertically movable pin 23 is moved in thefixed stage 21. As a result, the clearance between the disc substrate 1and the sheet 4 is gradually decreased. Finally, the disc substrate 1and the sheet 4 are press-fit. As a result, the plane of the informationsignal portion 1 c and the adhesive layer 2 b are adhered. After theyhave been stably press-fit, the movable stage 22 is moved so that it isapart from the fixed stage 21. Thereafter, with a predeterminedconveying device (not shown), the disc substrate 1 and the sheet 4 whichhave been press-fit are removed from the fixed stage 21.

[0101] As a result, the disc substrate 1 and the sheet 4 has beenadhered. An optical disc of which the light transmission layer 2 hasbeen formed on the plane of the information signal portion 1 c of thedisc substrate 1 has been produced.

[0102] The inventors of the present invention have produced varioustypes of disc substrates 1 in which the film thickness of the reactionprotection layer 15 had been varied and have compared them. In reality,as the replica substrate la, a polycarbonate (PC) substrate that has athickness of 1.1 mm and has a disc shape is used. As the informationsignal portion 1 c, a laminate film of a reflection layer 11 made of anAl alloy that has a film thickness of 100 nm, a first dielectric layer12 that has a film thickness of 18 nm and that is made of a mixture ofZnS and SiO₂ (ZnS—SiO₂), a recording layer 13 that has a film thicknessof 24 nm and that is made of a GeInSbTe alloy layer, a second dielectriclayer 14 that is made of ZnS—SiO₂, and a reaction protection layer 15that is made of a dielectric is used.

[0103] The film thickness of the second dielectric layer 14, made ofZnS—SiO₂, of the information signal portion 1 c is designated so thatthe reflectance of the mirror portion becomes 15% or larger. In otherwords, in grooves used to record/reproduce an information signal on theoptical disc, the reflectance of 10% or larger is required. Thereflectance of the grooves is around 70% of the reflectance of the flatmirror portion. Thus, to obtain good recording/reproducingcharacteristics on the grooves, the reflectance of the mirror portionshould be 15% or larger. In such a consideration, the inventors of thepresent invention have measured the film thickness dependency of thesecond dielectric layer (ZnS—SiO₂) to the reflectance.

[0104]FIG. 7 shows the measured results. As shown in FIG. 7, theinventors of the present invention have thought of the fact that as thefilm thickness of the second dielectric layer 14 increases, thereflectance varies in a sine wave shape. Thus, the film thickness of thesecond dielectric layer 14 is designated so that the reflectance, whichvaries in a sine wave shape, becomes 15% or larger. In reality, the filmthickness of the second dielectric layer 14 is designated in the rangefrom 45 to 90 nm or in the range from 130 to 175 nm. According to thefirst embodiment, the film thickness of the second dielectric layer 14is designated 140 nm.

[0105] The material of the reaction protection layer 15 of theinformation signal portion 1 c is decided in the following manner. Inother words, as described above, the light transmissivity sheet 2 a isadhered on the information signal portion 1 c through the adhesive layer2 b made of a pressure-sensitive adhesive agent (PSA). Thus, as thematerial of the reaction protection layer 15, which composes theoutermost layer of the information signal portion 1 c, a material thatdoes not chemically react with the adhesive layer 2 b is selected. Inreality, for example, silicon nitride is selected. According to thefirst embodiment, the reaction protection layer 15 is made of Si₃N₄.

[0106] A disc substrate 1 according to the first embodiment is a discsubstrate of which the outermost layer of the information signal portion1 c is the reaction protection layer 15 made of Si₃N₄. A disc substrate1 of which the film thickness of the reaction protection layer 15 is 1nm is referred to as disc substrate 1 of Example 1. A disc substrate 1of which the film thickness of the reaction protection layer 15 is 2 nmis referred to as disc substrate 1 of Example 2. A disc substrate 1 ofwhich the film thickness of the reaction protection layer 15 is 5 nm isreferred to as disc substrate 1 of Example 3. A disc substrate 1 ofwhich the film thickness of the reaction protection layer 15 is 10 nm isreferred to as disc substrate 1 of Example 4. A disc substrate 1 ofwhich the film thickness of the reaction protection layer 15 is 30 nm isreferred to as disc substrate 1 of Example 5.

[0107] A disc substrate 1 of which a disc shaped PC substrate that has athickness of 1.1 mm is used as the replica substrate la, the diameter(outer diameter) of the PC substrate is for example 120 mm, and theaperture (inner diameter) of the center hole 1 b is for example 15 mm isreferred to as disc substrate 1 of Comparative Example. The informationsignal portion 1 cof the conventional disc substrate 1 is composed of alaminate of a reflection layer made of an Al alloy having a filmthickness of 100 nm, a first dielectric layer made of ZnS—SiO₂ having afilm thickness of 18 nm, a phase change recording layer made of aGeInSbTe alloy having a film thickness of 24 nm, and a second dielectriclayer made of ZnS—SiO₂ having a film thickness of 140 nm. In otherwords, the disc substrate that does not have a reaction protection layer15 is referred to as disc substrate 1 of Comparative Example.

[0108] The rates of variation of reflectance of the optical discsproduced by the adhering method using the disc substrates 1 of Example 1to Example 5 and Comparative Example have been measured. First of all,the initial crystallizing process has performed for the optical discproduced with the disc substrates of Example 1 to Example 5 andComparative Example. As a result, the recording layer 13 of theinformation signal portion 1 c has been changed from the amorphous stateto the crystal state. Thereafter, the initial reflectance has beenmeasured. The optical discs have been placed in a constant-temperature,constant-humidity tank in which temperature has been kept at 80° C. andthe humidity has been kept at 85% for 1000 hours. In those conditions,acceleration tests have been performed. Thereafter, the reflectance ofthe optical discs taken from the constant-temperature, constant-humiditytank has been measured. Thereafter, the variation of reflectance beforeand after the acceleration tests has been measured. The reflectance hasbeen measured for a non-uneven portion of the optical discs namelymirror portion thereof using an evaluating system for an optical systemhaving a wavelength of 400 nm and a numerical aperture NA of 0.85. Therate of variation of reflectance has been obtained by dividing theamount of variation of reflectance of which the reflectance after theacceleration tests is subtracted from the initial reflectance by theinitial reflectance. Table 1 shows the measured results of the rates ofvariation of reflectance. TABLE 1 Comparative example Example 1 Example2 Example 3 Example 4 Example 5 Film thickness of Si₃N₄ 0 1 2 5 10 30[nm] Initial reflectance [%] 20.0 20.1 20.7 21.2 21.6 18.0 Reflectanceafter 14.3 17.2 18.8 19.9 20.8 17.8 acceleration test [%] Amount ofvariation of 5.7 2.9 1.9 1.3 0.8 0.2 reflectance [%] Amount of variationof 0.285 0.144 0.092 0.061 0.037 0.011 reflectance/ Initail reflectance

[0109] Table 1 shows that the amounts of variation of reflectance (ratesof variation of reflectance) to the initial reflectance of theacceleration tests for the optical discs produced with the discsubstrates 1 of Example 1 to Example 5 (namely, optical discs of Example1 to Example 5) are in the range from 0.011 to 0.144 and that the rateof variation of reflectance to the initial reflectance of theacceleration test for the optical disc produced with the disc substrate1 of Comparative Example (namely, optical disc of Comparative Example)is 0.285, which is around twice as large as that of Example 1. Inaddition, yellowish discoloring has been observed in the adhesive layer2 b of the optical disc of Comparative Example. The knowledge that theinventors of the present invention have obtained through the experimentsrepresents that the yellowish discoloring of the adhesive layer 2 b is acause of the decrease of the reflectance. Thus, with the reactionprotection layer 15 disposed at the interface with the adhesive layer 2b of the information signal portion 1 c, the reflectance can beprevented from deteriorating.

[0110] Table 1 also shows that in the optical discs of Example 1 toExample 5, since the rate of variation of reflectance of the opticaldisc of Example 1, where the film thickness of the reaction protectionlayer 15 made of Si₃N₄ is 1 nm, is 0.144 and the rate of variation ofreflectance of the optical disc of example 2, where the film thicknessof the reaction protection layer 15 is 2 nm, is 0.092, it is clear thatthe rate of variation of reflectance of the optical disc of Example 2decreases against that of the optical disc of Example 1. In other words,it is clear that the deterioration of the reflectance of the opticaldisc of Example 2 is suppressed against the optical disc of Example 1.When other examples are compared in the same manner, it is clear that asthe film thickness of the reaction protection layer 15 is increased, therate of variation of reflectance is decreased as with the optical discof Example 3 to the optical disc of Example 2; the optical disc ofExample 4 to the optical disc of Example 3; and the optical disc ofExample 5 to the optical disc of Example 4. In addition, the resultsthat the inventors of the present invention have observed the opticaldiscs of Example 1 to Example 5 represent that with the reactionprotection layer 15, the yellowing discoloring is decreased.

[0111] When the rate of variation of reflectance exceeds 0.1, therecording/reproducing characteristics of an information signal tend todeteriorate. Thus, the film thickness of the reaction protection layer15 made of Si₃N₄ should be larger than 1 nm, preferably 2 nm or larger.When the film thickness of the reaction protection layer 15 is 2 nm orlarger, it is certain that the rate of variation of reflectance is 0.1or smaller. As a result, good recording/reproducing characteristics areacquired.

[0112] As described above, in the optical disc and the producing methodthereof according to the first embodiment, since the reaction protectionlayer 15 made of Si₃N₄, which does not chemically react with theadhesive layer 2 b, is disposed as the outermost layer of theinformation signal portion 1 c on the lower main plane of the discsubstrate 1, when the optical disc is used for a long time, the adhesivelayer 2 b can be prevented from yellowish discoloring at the interfacewith the information signal portion 1 c. As a result, the decrease ofthe reflectance and the deterioration of the optical disc due to thediscoloring can be suppressed. Since the optical disc according to thefirst embodiment of the present invention has the light transmissionlayer, which is thin and which has small double refraction, hightransparency, and equal thickness, the optical disc conforms with alarge NA of an objective lens and has good recording/reproducingcharacteristics.

[0113] Next, an optical disc according to a second embodiment of thepresent invention will be described. Unlike with the optical discaccording to the first embodiment, in the optical disc according to thesecond embodiment, the reaction protection layer 15 is made of siliconoxide (SiO₂).

[0114] The material of the reaction protection layer 15 is decided inthe following manner. As described above, a light transmissivity sheet 2a is adhered to the outermost layer of an information signal portion 1 cthrough an adhesive layer 2 b made of a pressure-sensitive adhesiveagent (PSA). Thus, as the material of the reaction protection layer 15,which composes the outermost layer of the information signal portion 1c, a material that does not chemically react with the adhesive layer 2b, practically, for example silicon oxide, is selected. According to thesecond embodiment, the reaction protection layer 15 is made of SiO₂.

[0115] A disc substrate 1 according to the second embodiment, where theoutermost layer of the information signal portion 1 c is the reactionprotection layer 15 made of SiO₂, is hereinafter referred to as discsubstrate 1 of each of examples. A disc substrate 1 of which the filmthickness of the reaction protection layer 15 is 1 nm is referred to asdisc substrate 1 of Example 6. A disc substrate 1 of which the filmthickness of the reaction protection layer 15 is 2 nm is referred to asdisc substrate 1 of Example 7. A disc substrate 1 of which the filmthickness of the reaction protection layer 15 is 5 nm is referred to asdisc substrate 1 of Example 8. A disc substrate 1 of which the filmthickness of the reaction protection layer 15 is 10 nm is referred to asdisc substrate 1 of Example 9. A disc substrate 1 of which the filmthickness of the reaction protection layer 15 is 30 nm is referred to asdisc substrate 1 of Example 10. A disc substrate 1 used to compare thosedisc substrates 1 is the same as that according to the first embodiment.This disc substrate 1 is referred to as disc substrate 1 of ComparativeExample.

[0116] Since the other structure of the optical discs according to thesecond embodiment is the same as that according to the first embodiment,the description will be omitted. In addition, since the optical discproducing method according to the second embodiment is the same as thataccording to the first embodiment, the description will be omitted.

[0117] The rates of variation of reflectance of optical discs having thelight transmission layer formed by the adhering method according to thefirst embodiment with the disc substrates 1 of Example 6 to Example 10and Comparative Example have been measured.

[0118] In other words, the initial crystallizing process has beenperformed for the optical discs produced with the disc substrates 1 ofExample 6 to Example 10 and Comparative Example. As a result, therecording layer 13 of the information signal portion 1 c has beenchanged from the amorphous state to the crystal state. Thereafter, theinitial reflectance has been measured. The optical discs have beenplaced in a constant-temperature, constant-humidity tank in which thetemperature has been kept at 80° C. and the humidity has been kept at85% for 1000 hours. In those conditions, acceleration tests have beenperformed.

[0119] Thereafter, the reflectance of the optical discs taken from theconstant-temperature, constant-humidity tank has been measured.Thereafter, the variation of reflectance before and after theacceleration tests has been measured. The reflectance has been performedat a non-uneven portion namely mirror portion thereof using anevaluating device for an optical system having a wavelength of 400 nmand a numerical aperture NA of 0.85. Table 2 shows the measured resultsof the rates of variations of reflectance. TABLE 2 Comparative Exampleexample Example 6 Example 7 Example 8 Example 9 10 Film thickness ofSiO₂ 0 1 2 5 10 30 [nm] Initial reflectance [%] 20.0 20.1 20.6 21.1 21.318.4 Reflectance after 14.3 17.1 18.8 19.7 20.6 17.9 acceleration test[%] Amount of variation of 5.7 3.0 1.8 1.4 0.7 0.5 reflectance [%]Amount of variation of 0.285 0.149 0.087 0.066 0.033 0.027 reflectance/Initail reflectance

[0120] Table 2 shows that the amounts of variation of reflectance (ratesof variation of reflectance) to the initial reflectance of theacceleration tests for the optical discs produced with the discsubstrates 1 of Example 6 to Example 10 (namely, optical discs ofExample 6 to Example 10) are in the range from 0.027 to 0.149 and thatthe rate of variation of reflectance to the initial reflectance of theacceleration test for the optical disc produced with the disc substrate1 of Comparative Example (namely, optical disc of Comparative Example)is 0.285, which is around twice as large as that of Example 6. Inaddition, as described in the first embodiment, yellowish discoloringhas been observed in the adhesive layer 2 b of the optical disc ofComparative Example. The yellowish discoloring of the adhesive layer 2 bis a cause of the decrease of the reflectance. Thus, when the reactionprotection layer 15, which is made of SiO₂ and which does not chemicallyreact with the adhesive layer 2 b, is disposed at the interface with theadhesive layer 2 b of the information signal portion 1 c, thereflectance can be prevented from deteriorating.

[0121] Table 2 also shows that in the optical discs of Example 6 toExample 10, since the rate of variation of reflectance of the opticaldisc of Example 6, where the film thickness of the reaction protectionlayer 15 made of SiO₂ is 1 nm, is 0.149 and the rate of variation ofreflectance of the optical disc of Example 7, where the film thicknessof the reaction protection layer 15 is 2 nm, is 0.087, it is clear thatthe rate of variation of reflectance of the optical disc of Example 7decreases against that of the optical disc of Example 6. In other words,it is clear that the deterioration of the reflectance of the opticaldisc of Example 7 is suppressed against the optical disc of Example 6.When other examples are compared in the same manner, it is clear that asthe film thickness of the reaction protection layer 15 is increased, therate of variation of reflectance is decreased as with the optical discof Example 8 to the optical disc of Example 7; the optical disc ofExample 9 to the optical disc of Example 8; and the optical disc ofExample 10 to the optical disc of Example 9. In addition, the resultsthat the inventors of the present invention have observed the opticaldiscs of Example 6 to Example 10 represent that with the reactionprotection layer 15, the yellowing discoloring is decreased.

[0122] When the rate of variation of reflectance exceeds 0.1, therecording/reproducing characteristics of an information signal tend todeteriorate. Thus, the film thickness of the reaction protection layer15 made of SiO₂ should be larger than 1 nm, preferably 2 nm or larger.When the film thickness of the reaction protection layer 15 is 2 nm orlarger, it is certain that the rate of variation of reflectance is 0.1or smaller. As a result, good recording/reproducing characteristics areacquired.

[0123] In the optical disc and the producing method thereof according tothe second embodiment, since the reaction protection layer 15 made ofSiO₂, which does not chemically react with the adhesive layer 2 b, isdisposed as the outermost layer of the information signal portion 1 c onthe lower main plane of the disc substrate 1, the same effect as thefirst embodiment can be obtained.

[0124] Next, an optical disc according to a third embodiment of thepresent invention will be described. FIG. 8 shows the optical discaccording to the third embodiment of the present invention.

[0125] As shown in FIG. 8, unlike with the first embodiment, in theoptical disc according to the third embodiment, a reaction protectionresin layer 31 made of ultraviolet ray setting resin is formed so thatit coats an information signal portion 1 c. A light transmissivity sheet2 a is adhered to the front surface of the reaction protection resinlayer 31 through an adhesive layer 2 b. In such a manner, an opticaldisc is structured.

[0126] As shown in FIG. 9, unlike with the information signal portions 1c according to the first and second embodiments, the information signalportion 1 c according to the third embodiment does not have a reactionprotection layer 15. In the disc substrate 1 according to the thirdembodiment, a reaction protection resin layer 31 is formed on all onemain plane of a disc substrate 1. A disc substrate 1 that does not havethe reaction protection resin layer 31 is referred to as disc substrate1 of Comparative Example as with the first embodiment.

[0127] Next, an optical disc producing method according to the thirdembodiment will be described. On an uneven portion formed on one mainplane of a replica substrate 1 a that is the same as that according tothe first embodiment, a recording film, a reflection film, and so forthhave been formed. These films compose the information signal portion 1c.

[0128] As shown in FIG. 9, in the disc substrate 1 according to thethird embodiment, as the replica substrate la, a polycarbonate (PC)substrate that has a thickness of 1.1 mm and that has a disc shape isused. The diameter (outer diameter) of the PC substrate is for example120 mm. The aperture (inner diameter) of a center hole 1 b is forexample 15 mm. The information signal portion 1 c is a laminate film ofa reflection layer 11 made of an Al allow having a film thickness of 100nm, a first dielectric layer 12 that has a film thickness of 18 nm andthat is a mixture of ZnS and SiO₂, a phase change recording layer 13that has a film thickness of 24 nm and that is made of a GeSbTe alloylayer, and a second dielectric layer 14 made of a mixture (ZnS—SiO₂) ofzinc sulfide (ZnS) and silicon oxide (SiO₂) that are successivelylayered. As with the first embodiment, the film thickness of the seconddielectric layer 14 made of ZnS—SiO₂ is designated so that thereflectance of a mirror portion becomes 15% or larger. In reality, thefilm thickness of the second dielectric layer 14 is designated in therange from 45 to 90 nm or in the range from 130 to 175 nm. According tothe third embodiment, the film thickness of the second dielectric layer14 is designated 140 nm.

[0129] Since the sheet 4 is the same as those according to the first andsecond embodiments, the description thereof will be omitted.

[0130] Next, a method for forming the reaction protection resin layer 31according to the third embodiment will be described. FIG. 10 to FIG. 12show the method for forming the reaction protection resin layer 31according to the third embodiment.

[0131] As shown in FIG. 10, ultraviolet ray setting resin 32 is suppliedto and coated on one main plane of the information signal portion 1 c ofthe disc substrate 1. The ultraviolet ray setting resin 32 is suppliedfrom a nozzle opening of an ultraviolet ray setting resin supplyingportion 33 to the inner circumferential side of the disc substrate 1 sothat the ultraviolet ray setting resin 32 is formed in for example adisc shape.

[0132] Next, as shown in FIG. 11, the disc substrate 1 on which theultraviolet ray setting resin 32 has been coated is rotatedcounterclockwise (in the arrow direction M shown in FIG. 11) about arotating shaft (not shown) of the device. As a result, the ultravioletray setting resin 32 is fully coated on the front surface of the discsubstrate 1. Since the disc substrate 1 is rotated counterclockwise,excessive ultraviolet ray setting resin 32 is shaken off. As a result,the ultraviolet ray setting resin 32 is equally coated on theinformation signal portion 1 c of the replica substrate la. Thus, a filmhaving an equal thickness is formed. The film thickness of theultraviolet ray setting resin 32 that has been shaken off can beadjusted with the rotation speed.

[0133] Next, as shown in FIG. 12, the replica substrate 1 a on which theultraviolet ray setting resin 32 has been coated is placed in aradiation range of an ultraviolet ray light source 34 that can emit anultraviolet ray. At that point, the replica substrate 1 a is placed sothat the coated side of the ultraviolet ray setting resin 32 faces theultraviolet ray light source 34. Thereafter, an ultraviolet ray isradiated from the ultraviolet ray light source 34 to the ultraviolet raysetting resin 32 on the upper main plane of the replica substrate la. Atthat point, the cumulative intensity of the ultraviolet ray is forexample 500 mJ/cm². With the radiation of the ultraviolet ray, theultraviolet ray setting resin 32, which coats the information signalportion 1 c on the replica substrate 1 a, is hardened. As a result, thereaction protection resin layer 31 has been formed. Thus, the discsubstrate 1 according to the third embodiment has been produced.

[0134] The inventors of the present invention have formed the reactionprotection resin layers 31 on the disc substrates 1 produced by theforgoing producing method in various production conditions. A discsubstrate on which the reaction protection resin layer 31 has beenformed is referred to as disc substrate of each of examples.

[0135] First of all, as the ultraviolet ray setting resin 32 to becoated, with a resin that does not contain a solvent and whose viscosityis 4.0×10⁻² Pa·s (40 cps), the reaction protection resin layer 31 hasbeen formed on the replica substrate la. As a result, the disc substrate1 has been produced. At that point, the non-solvent type resin has beensupplied at a radial position of 17 mm of the replica substrate 1 a. Thedisc substrate 1 has been rotated at 83.3 s⁻¹ (5000 rpm) about therotating shaft. A disc substrate produced in a rotation time of 1 sec isreferred to as disc substrate 1 of Example 11. A disc substrate producedin a rotation time of 2 sec is referred to as disc substrate 1 ofExample 12. A disc substrate produced in a rotation time of 4 sec isreferred to as disc substrate 1 of Example 13. A disc substrate producedin a rotation time of 7 sec is referred to as disc substrate 1 ofExample 14. A disc substrate produced in a rotation time of 10 sec isreferred to as disc substrate 1 of Example 15. A disc substrate producedin a rotation time of 20 sec is referred to as disc substrate 1 ofExample 16.

[0136] In addition, as the ultraviolet ray setting resin 32 to becoated, with a solvent type resin that contains 50 weight % of methoxypropanol and that has a viscosity of 1.0×10⁻¹ Pa·s (10 cps), thereaction protection resin layer 31 has been formed on the replicasubstrate la. They have been left for 30 seconds. After the solve hadbeen fully given off, they have been hardened by the radiation of anultraviolet ray. As a result, the disc substrate 1 has been produced.The solvent type resin has been supplied at a radius position of 17 mmof the replica substrate la. The disc substrate 1 has been rotated aboutthe center of the rotating shaft in a rotation time of 83.3 s⁻¹ (5000rpm). A disc substrate produced in a rotation time of 1 sec is referredto as disc substrate 1 of Example 17. A disc substrate produced in arotation time of 2 sec is referred to as disc substrate 1 of Example 18.A disc substrate. produced in a rotation time of 4 sec is referred to asdisc substrate 1 of Example 19. A disc substrate produced in a rotationtime of 7 sec is referred to as disc substrate 1 of Example 20. A discsubstrate produced in a rotation time of 10 sec is referred to as discsubstrate 1 of Example 21. A disc substrate produced in a rotation timeof 20 sec is referred to as a disc substrate 1 of Example 22.

[0137] Table 3 shows film thickness characteristics of the reactionprotection resin layer 31 of the disc substrates 1 of Example 11 toExample 16 produced with the aforementioned non-solvent type ultravioletray setting resin 32 (namely, the average film thickness of the reactionprotection resin layer 31 in the data region of the disc substrates 1,the film thickness of the reaction protection resin layer 31 in theinner circumference of the data region (radius: 24 mm), the filmthickness of the reaction protection resin layer 31 in the outercircumference of the data region (radius: 58 mm), and the differencebetween the inner and outer circumferential film thicknesses. Table 4shows the results of the film thickness characteristics of the reactionprotection resin layer 31 of the disc substrates 1 of Example 17 toExample 22 produced with the ultraviolet ray setting resin 32, whichcontains a TABLE 3 Example Example Example Example Example Example 11 1213 14 15 16 Rotation time[s] 1 2 4 7 10 20 Average film thickness 7.65.8 4.3 3.0 2.7 1.9 [μm] Difference between 2.3 1.8 1.3 1.0 0.8 0.6inner and outer circumferential film thickness [μm]

[0138] TABLE 4 Example Example Example Example Example Example 17 18 1920 21 22 Rotation time[s] 1 2 4 7 10 20 Average film thickness 2.9 2.22.0 1.8 1.7 1.6 [μm] Difference between 0.4 0.3 0.2 0.2 0.1 0.1 innerand outer circumferential film thickness [μm]

[0139] Table 3 shows that when the reaction protection resin layer 31 isformed with the non-solvent type ultraviolet ray setting resin 32 by thespin coat method, as the rotation time is increased, the average filmthickness and the difference between the inner and outer circumferentialfilm thicknesses are decreased. Table 4 shows that when the reactionprotection resin layer 31 is formed with the ultraviolet ray settingresin 32 that contains a solvent by the spin coat method, as therotation time is increased, the average film thickness is decreased andthe difference between inner and outer circumferential film thicknessesbecomes very large in comparison with those of the disc substrates 1 ofExample 11 to Example 16. When the ultraviolet ray setting resin isformed by the spin coat method, the film thickness of the innercircumferential portion tends to be larger than the film thickness ofthe outer circumferential portion. Thus, it is preferred to use a resinthat contains a solvent as the ultraviolet ray setting resin 32. Withthe ultraviolet ray setting resin that contains the solvent, it is clearthat the difference between the inner and outer circumferential portionsof the data area becomes 1 μm or smaller.

[0140] As described above, after the reaction protection resin layer 31has been formed, the disc substrate 1 on which the reaction protectionresin layer 31 has been formed and the sheet 4 of the first embodimentare adhered by the adhering device of the first embodiment. As a result,the optical disc according to the third embodiment has been produced.

[0141] The inventors of the present invention have measured the initialreflectance and the reflectance after the acceleration tests for theoptical discs of which the sheet 4 has been adhered to the front surfaceof the reaction protection resin layer 31 of the disc substrates 1 ofExample 11 to Example 22 (these optical discs are referred to as opticaldiscs of Example 11 to Example 22) in the same manner as the firstembodiment and calculated the rates of variation of reflectance thereof.An optical disc of Comparative Example is the same as that of the firstembodiment. TABLE 5 Comparative Example Example Example Example ExampleExample example 11 12 13 14 15 16 Film thickness of 0 7.6 5.8 4.3 3.02.7 1.9 reaction protection resin layer [μm] Initial reflectance [%]20.0 18.8 18.9 19.1 19.3 19.5 19.5 Reflectance after 14.3 18.5 18.5 18.618.7 18.9 18.8 acceleration test [%] Amount of variation of 5.7 0.3 0.40.5 0.5 0.6 0.7 reflectance [%] Amount of variation of 0.285 0.016 0.0210.026 0.026 0.031 0.036 reflefctance/ Initail reflectance

[0142] TABLE 6 Comparative Example Example Example Example ExampleExample example 17 18 19 20 21 22 Film thickness of 0 2.9 2.2 2.0 1.81.7 1.6 reaction protection resin layer [μm] Initial reflectance [%]20.0 19.3 19.3 19.4 19.5 19.5 19.6 Reflectance after 14.3 18.8 18.8 18.818.9 18.8 18.8 acceleration test [%] Amount of variation of 5.7 0.5 0.50.6 0.6 0.7 0.8 reflectance [%] Amount of variation of 0.285 0.026 0.0260.031 0.031 0.036 0.041 reflectance/ Initail reflectance

[0143] Table 5 shows that the rate of variation of reflectance of theoptical disc of Comparative Example is 0.285 and that when at least thereaction protection resin layers 31 have been formed on the opticaldiscs of Example 11 to Example 16, the rates of variation of reflectancethereof can be decreased. In the optical disc of Comparative Example,yellowish discoloring has been observed. In the optical discs of Example11 to Example 16, discoloring of the adhesive layer 2 b has been hardlyobserved. The adhesive layer 2 b has been transparent.

[0144] When the rate of variation of reflectance exceeds 0.1, therecording/reproducing characteristics of an information signaldeteriorate. It is clear that the rate of variation of reflectance ofthe optical disc of Example 16 is 0.036, which is very small, althoughthe film thickness of the reaction protection resin layer 31 of Example16 is 1.9 μm, which is the smallest in the optical discs of Example 11to Example 16. Thus, it is clear that when the reaction protection resinlayer 31 is formed, it is certain that the rate of variation ofreflectance becomes 0.1 or smaller and thereby goodrecording/reproducing characteristics can be obtained.

[0145] Table 6 shows that the rate of variation of reflectance of theoptical disc of Comparative Example is 0.285 and that when at leastreaction protection resin layer 31 has been formed, the rate ofvariation of reflectance of the optical discs of Example 17 to Example22 can be decreased. In the optical disc of Comparative Example,yellowish discoloring has been observed. However, in the optical discsof Example 17 to Example 22, discoloring of the adhesive layer 2 b ofthe optical discs has been hardly observed. The adhesive layer 2 b hasbeen transparent.

[0146] It is clear that the rate of variation of reflectance of theoptical disc of Example 22 is 0.041, which is very small, although thefilm thickness of the reaction protection resin layer 31 of Example 22is 1.6 am, which is the smallest in the optical discs of Example 17 toExample 22. Thus, it is clear that when the reaction protection resinlayer 31 is formed, it is certain that the rate of variation ofreflectance becomes 0.1 or smaller and thereby goodrecording/reproducing characteristics can be obtained.

[0147] In the optical disc according to the third embodiment of thepresent invention, since the ultraviolet ray setting resin is coated andhardened on the replica substrate 1 a so that the ultraviolet raysetting resin fully coats the information signal portion 1 c. As aresult, the reaction protection resin layer 31 is formed. The lighttransmission layer 2 is formed through the reaction protection resinlayer 31. As a result, the same effect as the first embodiment can beobtained.

[0148] When the optical disc according to the third embodiment isproduced, the ultraviolet ray setting resin 32 that contains a solventis coated on the reaction protection resin layer 31 by the spin coatmethod. Thus, the light transmission layer of which the differencebetween the inner and outer circumferential film thicknesses of the dataregion is small can be formed. Consequently, an optical disc having goodrecording/reproducing characteristics can be produced.

[0149] So far, embodiments of the present invention have beenpractically described. However, the present invention is not limited tothose. Instead, there are various modifications of the present inventionwithout departing from the spirit thereof.

[0150] For example, numerical values, materials, structures of opticaldiscs that have been described in the forgoing embodiments are justexamples. When necessary, different numerical values, materials, andstructures of optical discs may be used.

[0151] In the forgoing embodiments, the present invention is applied tooptical discs having a light transmission layer. In addition, thepresent invention can be applied to optical hard disks and removableoptical hard disks that use magneto-optical recording and reproducing.According to the forgoing first embodiment, the present invention isapplied to a phase change type optical disc, where an information signalis recorded using a phase change. However, the present invention can beapplied to other rewritable optical disc, a write once type opticaldisc, or a read only type optical disc without departing from the spiritof the present invention.

[0152] When two optical discs of an embodiment of the present inventionare adhered so that their light transmission layers 2 face outside, adouble-sided optical disc can be produced.

[0153] In addition, according to the first embodiment, an example ofwhich an information signal portion is formed on a substrate has beendescribed. Alternatively, the information signal portion may be formedon a sheet so that the information signal portion faces the substrate.The sheet may be made of a plurality of thin films. The outermost layermay be unevenly formed as the information signal portion.

[0154] As described above, according to the present invention, since areaction protection layer is formed on an adhesive layer side of theinformation signal portion, the information signal portion on one mainplane of the substrate can be prevented from chemically reacting withthe adhesive layer of the light transmission layer. Thus, in the opticaldisc of which the light transmissivity sheet has been adhered to onemain surface of the substrate through the adhesive layer, the variationof reflectance of each optical disc can be suppressed. In addition, thevariation of reflectance of the recording/reproducing plane of theoptical disc can be suppressed. Moreover, the optical disc can conformwith a large NA of an objective lens used to record/reproduce data. Theoptical disc has a light transmission layer that has small doublerefraction, high transparency, and equal film thickness. In addition,the production yield of the optical disc can be improved.

1. (amended) An optical disc having an information signal portioncomposed of a plurality of layers and configured to record and/orreproduce an information signal and a light transmission layerconfigured to transmit laser light used to record and/or reproduce theinformation signal, the information signal portion and the lighttransmission layer being formed on one main plane of a substrate of theoptical disc, wherein the light transmission layer comprises at least asheet having light transmissivity and an adhesive layer made of apressure-sensitive adhering agent for adhering the sheet to the mainplane of the substrate, wherein the film thickness of the lighttransmission layer is in the range from 90 μm to 110 μm, and wherein areaction protection layer made of the dielectric of silicon nitride orsilicon oxide is formed on the information signal portion so that thereaction protection layer faces the adhesive layer.
 2. (canceled) 3.(canceled)
 4. (amended) The optical disc as set forth in claim 1,wherein the film thickness of the reaction protection layer made ofsilicon nitride or silicon oxide is in the range from 2 nm to 30 nm. 5.(canceled)
 6. (canceled)
 7. (canceled)
 8. (canceled)
 9. The optical discas set forth in claim 1, wherein the film thickness of the informationsignal portion is in the range from 183 nm to 313 nm.
 10. (amended) Anoptical disc having an information signal portion composed of aplurality of layers and configured to record and/or reproduce aninformation signal and a light transmission layer configured to transmitlaser light used to record and/or reproduce the information signal, theinformation signal portion and the light transmission layer being formedon one main plane of a substrate of the optical disc, wherein the lighttransmission layer comprises at least a sheet having lighttransmissivity and an adhesive layer configured to adhere the sheet tothe main plane of the substrate, wherein the film thickness of the lighttransmission layer is in the range from 90 μm to 110 μm, and wherein areaction protection layer made of an ultraviolet ray setting resin isformed between the information signal portion and the adhesive layer.11. (canceled)
 12. (canceled)
 13. The optical disc as set forth in claim10, wherein the distribution of the film thickness of the reactionprotection layer in a region of at least the information signal portionis 1 μm or smaller.
 14. (canceled)
 15. The optical disc as set forth inclaim 10, wherein the film thickness of the information signal portionis in the range from 183 nm to 313 nm.
 16. (amended) An optical dischaving an information signal portion configured to record and/orreproduce an information signal and a light transmission layerconfigured to transmit laser light used to record and/or reproduce theinformation signal, the information signal portion and the lighttransmission layer being formed on one main plane of a substrate of theoptical disc, wherein the light transmission layer comprises at least asheet having light transmissivity and an adhesive layer configured toadhere the sheet to the main plane of the substrate, wherein theinformation signal portion comprises at least a reflection layerconfigured to reflect-the laser light, a first dielectric layer, arecording layer configured to record the information signal, and asecond dielectric layer successively formed from the substrate, andwherein the second dielectric layer is made of a mixture of zinc sulfideand silicon oxide, and in case that the film thickness of the seconddielectric layer is in the range from 45 nm to 90 nm or from 130 nm to175 nm, the film thickness of the second dielectric layer is designatedso that the reflectance of the laser light on a flat plane of thesubstrate is 15% or larger.
 17. (canceled)
 18. (canceled)
 19. (canceled)20. (amended) An optical disc producing method, comprising the steps of:forming an information signal portion configured to record and/orreproduce an information signal on a main plane of a substrate; andadhering a light transmissivity sheet configured to transmit laser lightused to record and/or reproduce the information signal in a region thatcovers the information signal portion through an adhesive layer, whereinthe adhesive layer is made of a pressure-sensitive adhering agent,wherein the film thickness of the light transmission layer is in therange from 90 μm to 110 μm, and wherein a reaction protection layer madeof the dielectric of silicon oxide or silicon nitride is formed on theoutermost layer of the information signal portion.
 21. (canceled) 22.(canceled)
 23. (amended) The optical disc producing method as set forthin claim 20, wherein the film thickness of the reaction protection layermade of silicon oxide or silicon nitride is in the range from2 nm to 30nm.
 24. (canceled)
 25. (canceled)
 26. (canceled)
 27. (canceled)
 28. Theoptical disc producing method as set forth in claim 20, wherein the filmthickness of the information signal portion is in the range from 183 nmto 313 nm.
 29. (amended) An optical disc producing method, comprisingthe steps of: forming an information signal portion configured to recordand/or reproduce an information signal on a main plane of a substrate;and adhering a light transmissivity sheet configured to transmit laserlight used to record and/or reproduce the information signal in a regionthat covers the information signal portion through an adhesive layer,wherein after the information signal portion forming step, before thelight transmissivity sheet adhering step, a reaction protection layermade of an ultraviolet ray setting resin is formed on at least an upperlayer of the information signal portion, and wherein the film thicknessof the light transmission layer is in the range from 90 μm to 110 μm.30. (canceled)
 31. (canceled)
 32. The optical disc producing method asset forth in claim 29, wherein the distribution of the film thickness ofthe reaction protection layer in a region of at least the informationsignal portion is 1 μm or smaller.
 33. (canceled)
 34. The optical discproducing method as set forth in claim 29, wherein the film thickness ofthe information signal portion is in the range from 183 nm to 313 nm.35. (added) The optical disc as set forth in claim 10, wherein thereaction protection layer is formed by coating ultraviolet ray settingresin that contains a solvent on the information signal portion by thespin coat method, giving off the solvent that is contained in theultraviolet ray setting resin, and hardening the ultraviolet ray settingresin that gave off the solvent.
 36. (added) The optical disc as setforth in claim 35, wherein the solvent is methoxypropanol.
 37. (added)The optical disc producing method as set forth in claim 29, wherein thereaction protection layer is formed by coating ultraviolet ray settingresin that contains a solvent on the information signal portion by thespin coat method, giving off the solvent that is contained in theultraviolet ray setting resin, and hardening the ultraviolet ray settingresin that gave off the solvent.
 38. (added) The optical disc producingmethod as set forth in claim 37, wherein the solvent is methoxypropanol.